Seabird Community Research Articles

A preliminary analysis of the distribution and spatial/temporal patterns of seabirds in the Laje de Santos Marine State Park (Santos, Brazil) and surrounding waters

Abstract This study investigates the temporal taxonomic variation of the seabird community, and the spatial distributions of seabirds in the Laje de Santos Marine State Park (PEMLS) and surrounding waters, based on shipboard surveys. The increase in the number of seabird taxa during winter is associated to the presence of migratory birds from the south. During summer, only resident species were observed within the park. Analysis of the spatial distributions of taxa using geographic information systems (GIS) identified three different regions within the study area. The first was close to the coast, where birds interact with fishing activities in search for food; the second was the nesting area that provides shelter for the breeding colonies; and the third, which is farther offshore and more exposed, where a higher number of migratory birds were observed during winter surveys. The PEMLS and surrounding waters have characteristics that are important for the study and preservation of seabirds in Brazil and for the South Atlantic Ocean.

Ecosystem variability in the offshore northeastern Chukchi Sea

Understanding influences of cumulative effects from multiple stressors in marine ecosystems requires an understanding of the sources for and scales of variability. A multidisciplinary ecosystem study in the offshore northeastern Chukchi Sea during 2008–2013 investigated the variability of the study area’s two adjacent sub-ecosystems: a pelagic system influenced by interannual and/or seasonal temporal variation at large, oceanographic (regional) scales, and a benthic-associated system more influenced by small-scale spatial variations. Variability in zooplankton communities reflected interannual oceanographic differences in waters advected northward from the Bering Sea, whereas variation in benthic communities was associated with seafloor and bottom-water characteristics. Variations in the planktivorous seabird community were correlated with prey distributions, whereas interaction effects in ANOVA for walruses were related to declines of sea-ice. Long-term shifts in seabird distributions were also related to changes in sea-ice distributions that led to more open water. Although characteristics of the lower trophic-level animals within sub-ecosystems result from oceanographic variations and interactions with seafloor topography, distributions of apex predators were related to sea-ice as a feeding platform (walruses) or to its absence (i.e., open water) for feeding (seabirds). The stability of prey resources appears to be a key factor in mediating predator interactions with other ocean characteristics. Seabirds reliant on highly-variable zooplankton prey show long-term changes as open water increases, whereas walruses taking benthic prey in biomass hotspots respond to sea-ice changes in the short-term. A better understanding of how variability scales up from prey to predators and how prey resource stability (including how critical prey respond to environmental changes over space and time) might be altered by climate and anthropogenic stressors is essential to predicting the future state of both the Chukchi and other arctic systems.

Inter-specific niche partitioning and overlap in albatrosses and petrels: dietary divergence and the role of fishing discards

Although fisheries discards are recognized as a key food source for many seabirds, there have been few thorough assessments of their importance relative to natural prey, and of their influence on the trophic structure of pelagic seabird communities during the non-breeding period. Competition for resources in Procellariiformes appears to be reduced mainly by avoiding spatial overlap, which is supposed to influence diet composition. However, artificial food sources provided by fisheries might relax niche partitioning, increasing trophic niche overlap. Using bycaught birds from pelagic longline fisheries, we combined the conventional diet and stable isotope analyses to assess the importance of fishing discards in the diet of eight species of Procellariiformes. Both methods revealed the high contribution of trawl discards to the non-breeding diet of three neritic species and a moderate contribution in several other species; discards from pelagic and demersal longline fisheries were considerably less important. There was a clear contrast in diets of neritic vs. oceanic species, which are closely related taxonomically, but segregate at sea. Niche partitioning was less clear among neritic species. They showed an unexpectedly high level of diet overlap, presumably related to the large volume of trawl discards available. This is the first study combining the conventional diet and stable isotope analyses to quantify the importance of fishery discards for a community of non-breeding seabirds, and demonstrates how the super-abundance of supplementary food generates high levels of overlap in diets and allows the coexistence of species.

Sea ice phenology and primary productivity pulses shape breeding success in Arctic seabirds

Spring sea ice phenology regulates the timing of the two consecutive pulses of marine autotrophs that form the base of the Arctic marine food webs. This timing has been suggested to be the single most essential driver of secondary production and the efficiency with which biomass and energy are transferred to higher trophic levels. We investigated the chronological sequence of productivity pulses and its potential cascading impacts on the reproductive performance of the High Arctic seabird community from Svalbard, Norway. We provide evidence that interannual changes in the seasonal patterns of marine productivity may impact the breeding performance of little auks and Brünnich’s guillemots. These results may be of particular interest given that current global warming trends in the Barents Sea region predict one of the highest rates of sea ice loss within the circumpolar Arctic. However, local- to regional-scale heterogeneity in sea ice melting phenology may add uncertainty to predictions of climate-driven environmental impacts on seabirds. Indeed, our fine-scale analysis reveals that the inshore Brünnich’s guillemots are facing a slower advancement in the timing of ice melt compared to the offshore-foraging little auks. We provide a suitable framework for analyzing the effects of climate-driven sea ice disappearance on seabird fitness.

Four sympatrically nesting auks show clear resource segregation in their foraging environment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 572:243-254 (2017) - DOI: https://doi.org/10.3354/meps12144 Four sympatrically nesting auks show clear resource segregation in their foraging environment Isabeau Pratte1,*, Gregory J. Robertson2, Mark L. Mallory1 1Department of Biology, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada 2Wildlife Research Division, Environment and Climate Change Canada, Mount Pearl, Newfoundland A1N 4T3, Canada *Corresponding author: pratteisabeau@gmail.com ABSTRACT: Auks share ecological similarities and are often found in sympatrically nesting assemblages at suitable nesting sites. It is expected that co-existing species would have evolved strategies to reduce niche overlap in response to resource competition. The presence of Atlantic puffins Fratercula arctica, razorbills Alca torda, thick-billed murres Uria lomvia and common murres U. aalge at the Gannet Islands, Labrador, is an opportunity to study interspecific interactions in a major seabird community. We compared the foraging movements of adult breeding birds and the diet of the birds inferred through (1) stable isotopes in the blood of adults, and (2) prey delivered to the chicks, as dimensions in the foraging niche among these 4 auks. Our results revealed that puffins and thick-billed murres headed offshore to forage, while razorbills and common murres were more coastal, heading towards mainland Labrador. The patterns of spatial segregation found among coastal and pelagic birds were mirrored by their stable isotope ratios, with one group of species foraging at a higher trophic level of an inshore food web and the other foraging on a lower trophic level of an offshore, pelagic food web. The ‘pelagic’ species segregated by prey choice for their chicks while differential alternate prey selection was the source of segregation between the ‘coastal’ species. Our research highlights the importance of segregation patterns in both spatial and diet dimensions of the foraging niche among the 4 auks—a potential mechanism for reducing interspecific competition among ecologically similar seabirds and explaining the persistence of such seabird assemblages through time. KEY WORDS: Seabird · Foraging distribution · Niche overlap · Diet · Isotopic niche Full text in pdf format Supplementary material PreviousNextCite this article as: Pratte I, Robertson GJ, Mallory ML (2017) Four sympatrically nesting auks show clear resource segregation in their foraging environment. Mar Ecol Prog Ser 572:243-254. https://doi.org/10.3354/meps12144 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 572. Online publication date: May 31, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Seabirds At-Sea Surveys: The Line-Transect Method Outperforms the Point-Transect Alternative

Introduction:Knowledge of seasonal distribution and abundance of species is paramount in identifying key areas. Field data collection and analysis must provide best information concerning seabirds at-sea to optimize conservation efforts.Methods:We tested whether modeling of detection probabilities, and density estimates with their coefficients of variation obtained from the point-transect method provided more robust and precise results than the more commonly used line-transect method. We subdivided our data by species groups (alcids, and aerialist species), and into two behavior categories (flyingvs.swimming). We also computed density estimates from the strip-transect and point count methods, to relate differences between transect methods to their counterparts that do not consider a decreasing probability of detection with distance from the observer. We used data collected in the Gulf of St. Lawrence between 2009 and 2010 when observers simultaneously conducted line- and point-transect sampling.Results:Models of detection probability using the line-transect method had a good fit to the observed data, whereas detection probability histograms of point-transect analyses suggested substantial evasive movements within the 0-50 m interval. This resulted in point-transect detection probability models displaying poor goodness of fit. Line transects yielded density estimates 1.2-2.6 times higher than those obtained using the point-transect method. Differences in percent coefficients of variation between line-transect and point-transect density estimates ranged between 0.2 and 5.9.Conclusion:Using 300 m wide line-transects provided the best results, while other methods could lead to biased conclusions regarding species density in the local landscape and the relative composition of seabird communities among species and behavior groups.

Trophic ecology drives contaminant concentrations within a tropical seabird community

To support environmental management programs, there is an urgent need to know about the presence and understand the dynamics of major contaminants in seabird communities of key marine ecosystems. In this study, we investigated the concentrations and trophodynamics of trace elements in six seabird species and persistent organic pollutants (POPs) in three seabird species breeding on Grand Connétable Island (French Guiana), an area where the increase in human population and mining activities has raised concerns in recent years. Red blood cell Hg concentrations in adults were the highest in Magnificent frigatebirds Fregata magnificens (median: 5.6 μg g−1 dw; range: 3.8–7.8 μg g−1 dw) and lowest in Sooty terns Onychoprion fuscatus (median: 0.9 μg g−1 dw; range: 0.6–1.1 μg g−1 dw). Among POPs, dichlorodiphenyldichloroethylene (p,p’-DDE) was the most abundant compound in plasma of Cayenne terns Thalasseus sandvicensis (median: 1100 pg g−1 ww; range: 160 ± 5100 pg g−1 ww), while polychlorinated biphenyls (PCBs) were the most abundant compound class in plasma of Magnificent frigatebirds (median: 640 pg g−1 ww; range 330 ± 2700 pg g−1 ww). While low intensity of POP exposure does not appear to pose a health threat to this seabird community, Hg concentration in several adults Laughing gulls Leucophaeus atricilla and Royal terns Thalasseus maximus, and in all Magnificent frigatebirds was similar or higher than that of high contaminated seabird populations. Furthermore, nestling red blood cells also contained Hg concentrations of concern, and further studies should investigate its potential health impact in this seabird community. Differences in adult trophic ecology of the six species explained interspecific variation in exposure to trace element and POPs, while nestling trophic ecology provides indications about the diverse feeding strategies adopted by the six species, with the consequent variation in exposure to contaminants.

Habitat modelling predictions highlight seasonal relevance of Marine Protected Areas for marine megafauna

According to the European Union Habitats and Birds Directives, EU Member States must extend the Natura 2000 network to marine ecosystems, through the designation of Marine Protected Areas (MPAs). However, the initial status of cetacean and seabird communities across European waters is often poorly understood. It is assumed that an MPA is justified where at least 1% of the “national population” of a species is present during at least part of its biological cycle. The aim of the present work was to use model-based cetacean and seabird distribution to assess the networks of existing Natura 2000 sites and offshore proposed areas of biological interest. The habitat models used here were Generalised Additive Models computed from aerial surveys observational data collected during the winter 2011–2012 and the summer 2012 across the English Channel, Bay of Biscay and north-western Mediterranean Sea. Based on these models, a ratio between species relative abundance predicted within each MPA and the total relative abundance predicted over the French Atlantic or Mediterranean marine regions was computed and compared to the 1% threshold. This assessment was conducted for winter and summer independently, providing information for assessing the relevance of individual MPAs and MPA networks at a seasonal scale. Our results showed that the existing network designed for coastal seabird species was relevant in both marine regions. In contrast, a clear shortfall was identified for offshore seabird species in the Atlantic region and for cetaceans in both regions. Moreover, the size of MPAs appeared to be a crucial feature, with larger MPAs being relevant for more species. Finally, we showed that the proposed large offshore areas of interest would constitute a highly relevant network for all offshore species, with e.g. up to 61% of the Globicephalinae population in the Atlantic French waters being present within these areas.

A specimen-based approach to reconstructing the late Neogene seabird communities of California

California has experienced major climate change from the early Miocene (~23Ma) to the present. Fossil seabirds are useful for studying marine faunal responses to these changes because they are numerous in museum collections and easily identified to the family-level from fragmentary remains. Because extant seabirds respond quickly to environmental changes, we hypothesize that the fossil record of crown-group Miocene seabirds will reflect past environments. Previous studies of fossil seabird diversity through the Cenozoic of the North Pacific relied mainly on literature records to describe the appearance and disappearance of seabird species and correlated these patterns to geologic and climatic events. Our study uses an empirical, specimen-based approach to describe the seabird response to climate and tectonic change during ~12 million years of coastal California's geologic history (middle Miocene to early Pliocene). The foundation of our dataset is 242 fossil seabird specimens from Orange County. The strata from Orange County form the basis for delineating chronostratigraphic bins used for studying 285 additional seabird fossils from other parts of California, for a total of 527 seabird fossils examined. Our results show a relationship between pelagic seabirds and offshore facies as well as a clear increase of pan-alcid abundance and decline of sulid abundance through time. This pattern may be the result of taphonomic bias combined with the effect of shallower facies preserved through time. The increase in pan-alcid abundance is also coincident with global climatic and tectonic changes and with enhanced and stable nutrient upwelling. Upwelling through this time also helps to explain morphological changes in salmon and speciation rates in marine mammals. The specimen-based methodology used here can be applied to contemporaneous taxa, such as marine mammals, to quantitatively analyze diversity during the late Neogene and further explore the relationship between physical drivers and faunal change.

WITHDRAWN: A specimen-based approach to reconstructing the late Neogene seabird communities of California

WITHDRAWN: A specimen-based approach to reconstructing the late Neogene seabird communities of California

Using large scale surveys to investigate seasonal variations in seabird distribution and abundance. Part II: The Bay of Biscay and the English Channel

Seabird distributions and the associated seasonal variations remain challenging to investigate, especially in oceanic areas. Recent advances in telemetry have provided considerable information on seabird ecology, but still exclude small species, non-breeding birds and individuals from inaccessible colonies from any scientific survey. To overcome this issue and investigate seabird distribution and abundance in the eastern North Atlantic (ENA), large-scale aerial surveys were conducted in winter 2011-12 and summer 2012 over a 375,000km2 area encompassing the English Channel (EC) and the Bay of Biscay (BoB). Seabird sightings, from 15 taxonomic groups, added up to 17,506 and 8263 sightings in winter and summer respectively, along 66,307km. Using geostatistical methods, density maps were provided for both seasons. Abundance was estimated by strip transect sampling. Most taxa showed marked seasonal variations in their density and distribution. The highest densities were recorded during winter for most groups except shearwaters, storm-petrels, terns and large-sized gulls. Subsequently, the abundance in winter nearly reached one million individuals and was 2.5 times larger than in summer. The continental shelf and the slope in the BoB and the EC were identified as key areas for seabird conservation, especially during winter, as birds from northern Europe migrate southward after breeding. This large-scale study provided a synoptic view of the seabird community in the ENA, over two contrasting seasons. Our results highlight that oceanic areas harbour an abundant avifauna. Since most of the existing marine protected areas are restricted to the coastal fringe, the importance of oceanic areas in winter should be considered in future conservation plans. Our work will provide a baseline for the monitoring of seabird distribution at sea, and could inform the EU Marine Strategy Framework Directive.

Using large scale surveys to investigate seasonal variations in seabird distribution and abundance. Part I: The North Western Mediterranean Sea

Scientific investigation in offshore areas are logistically challenging and expensive, therefore the available knowledge on seabird at sea distribution and abundance, as well as their seasonal variations, remains limited. To investigate the seasonal variability in seabird distribution and abundance in the North-Western Mediterranean Sea (NWMS), we conducted two large-scale aerial surveys in winter 2011–12 and summer 2012, covering a 181,400km2 area. Following a strip-transect method, observers recorded a total of 4141 seabird sightings in winter and 2334 in summer, along 32,213km. Using geostatistical methods, we generated sightings density maps for both seasons, as well as estimates of density and abundance. Most taxa showed seasonal variations in their density and distribution patterns, as they used the area either for wintering or for breeding. Highest densities of seabirds were recorded during winter, although large-sized shearwaters, storm petrels and terns were more abundant during summer. Consequently, with nearly 170,000 seabirds estimated in winter, the total abundance was twice higher in winter. Coastal waters of the continental shelf were generally more exploited by seabirds, even though some species, such as Mediterranean gulls, black-headed gulls, little gulls and storm petrels were found at high densities in highly offshore waters. Our results revealed areas highly exploited by the seabird community in the NWMS, such as the Gulf of Lion, the Tuscan region, and the area between Corsica and Sardinia. In addition, these large-scale surveys provide a baseline for the monitoring of seabird at sea distribution, and could inform the EU Marine Strategy Framework Directive.

Favorites and leftovers on the menu of scavenging seabirds: modelling spatiotemporal variation in discard consumption

Fishery discards subsidise the food supply of a large community of scavenging seabirds, thus substantially influencing seabird ecology. Seabird preference for certain types of discards determines the number and composition of discards available for non-avian marine scavengers. To quantify both portions of discards temporally as well as spatially, we have used a modelling framework that integrates the spatial and temporal variation in seabird distribution, seabird attraction to fishing vessels, and discard distribution. The framework was applied to a case study in the Bay of Biscay, where a wide variation in discard consumption was observed across seabird foraging guilds, discard types, periods, and locations. Seabirds removed about one-quarter of the Bay of Biscay discards. The remaining sinking discards have limited potential to subsidize scavenging benthic communities on a large scale, but they may contribute substantially to scavenger diets on a local scale. Changes in food subsidies caused by discard mitigation measures, such as the “landing obligation” in the European Common Fisheries Policy, are likely to have ecosystem effects on both scavenging seabirds and non-avian marine scavengers.

Long-term trends (1989-2013) in the seabird community breeding in the lagoon of Venice (Italy)

The community of seabirds breeding in the lagoon of Venice, one of the largest around the Mediterranean, was monitored over the 1989-2013 period. Six species have been recorded (<em>Larus michahellis, Chroicocephalus ridibundus, Larus melanocephalus, Sternula albifrons, Sterna hirundo, Sterna sandvicensis</em>). Over the study period, 346 colonies were surveyed; they were located on saltmarsh islets, dredge islands and other artificial sites, in descending order of importance. Beaches were used only at the beginning of the survey. About 4,900 pairs bred in the 2009-2013 years. The community has been always dominated by <em>L</em>. <em>michahellis</em>; in the 2009-2013, this species and <em>S. sandvicensis</em> comprised about 70% of the total. The longterm trends show moderate increase in the size of the whole community. Contrasting trends were observed in different species, with <em>L. michahellis</em>,<em> S. albifrons</em> and <em>S. sandvicensis</em> stable or increasing, whereas <em>C. ridibundus</em> and <em>S. hirundo</em> were declining. The number of pairs nesting on artificial sites increased over the last 15 years, while those on saltmarsh islets decreased correspondingly. This was possibly a response to the increase of mean sea level and storminess observed in the last twenty-five years. <em>S. albifrons</em> and <em>S. sandvicensis</em> populations reached national importance; the population of the latter species is noteworthy at a Mediterranean level.

How does ocean seasonality drive habitat preferences of highly mobile top predators? Part II: The eastern North-Atlantic

Marine ecosystems are characterised by strong heterogeneity and variability, both spatially and temporally. In particular, seasonal variations may lead to severe constraints for predators which have to cope with these variations, for example through migration to avoid unfavourable seasons, or adaptation to local modification of the ecosystem. In the Bay of Biscay and English Channel, ecosystem seasonality is well marked, especially over the shelf. Cetacean and seabird communities within the Bay of Biscay, Celtic Sea and English Channel were studied during aerial surveys conducted in winter 2011–2012 and summer 2012, following a strip-transect methodology deployed from the coast to oceanic waters. We explored seasonal variations of habitat preferences of four cetacean and six seabird groups through Generalised Additive Models, using physiographic variables and weekly- and monthly-averaged oceanographic predictors for both seasons. Our results provided the first overview at such a large scale of the variation of habitat preferences in response to the seasonality of the ocean by seabirds in that region, at such a large scale. Habitat models resulted in explained deviances from 13 to 55%. Predators answered the seasonality of their environment in different ways. Long-finned pilot whales and Risso׳s dolphins were the only studied group exhibiting no habitat variations between seasons, targeting the shelf break throughout the year. The other groups modulated their habitat preferences between seasons to optimise the compromise between the ocean seasonal variations and their own constraints: common and striped dolphins, bottlenose dolphins and harbour porpoises for cetaceans; northern gannets, auks, northern fulmars and kittiwakes for seabirds. For shearwaters, the seasonality had an extreme impact, inducing a complete absence from the region during the unfavourable season.

Temporal shifts in seabird populations and spatial coherence with prey in the southeastern Bering Sea

The Bering Sea is a highly productive ecosystem with abundant prey populations in the summer that support some of the largest seabird colonies in the Northern Hemisphere. In the fall, the Bering Sea is used by large numbers of migrants and post-breeding seabirds. We used over 22 000 km of vessel-based surveys carried out during summer (June to July) and fall (late August to October) from 2008 to 2010 over the southeast Bering Sea to examine annual and seasonal changes in seabird communities and spatial relationships with concurrently sampled prey. Deep-diving murres Uria spp., shallow-diving shearwaters Ardenna spp., and surface-foraging northern fulmars Fulmarus glacialis and kittiwakes Rissa spp. dominated summer and fall seabird communities. Sea- bird densities in summer were generally less than half of fall densities and species richness was lower in summer than in fall. Summer seabird densities had high interannual variation (highest in 2009), whereas fall densities varied little among years. Seabirds were more spatially clustered around breeding colonies and the outer continental shelf in the summer and then dispersed throughout the middle and inner shelf in fall. In summer, the abundance of age-1 walleye pollock Gadus chal co - grammus along with spatial (latitude and longitude) and temporal (year) variables best explained broad-scale seabird distribution. In contrast, seabirds in fall had weaker associations with spatial and temporal variables and stronger associations with different prey species or groups. Our results demonstrate seasonal shifts in the distribution and foraging patterns of seabirds in the southeastern Bering Sea with a greater dependence on prey occurring over the middle and inner shelf in fall.

Ecological shift from piscivorous to planktivorous seabirds in the Chukchi Sea, 1975–2012

Sea ice now forms later and melts earlier than it did 4 decades years ago, and it now melts completely in all parts of the Chukchi Sea. This decline in sea ice is expected to have repercussions on the trophic structure in this environment, and there are indications that changes already have taken place in the seabird community. We compared boat-based densities of seabirds in the eastern Chukchi Sea between July and October during 1975–1981 (historical data) with densities during 2007–2012 (recent data). We related the composition of the seabird community to sea-ice cover to explore how the community may be responding to changes in oceanography. The seabird community historically was composed predominantly of piscivorous Black-legged Kittiwakes (Rissa tridactyla) and murres (Uria spp.). In contrast, the seabird community now is composed predominantly of planktivorous seabirds such as Crested Auklets (Aethia cristatella) and Short-tailed Shearwaters (Puffinus tenuirostris). Total abundance of seabirds declined in three of four strata in the eastern Chukchi Sea, largely due to declines in densities of piscivorous and omnivorous species. These changes in the abundance and community composition of seabirds were associated with changes in ice cover. Earlier ice retreat appears to contribute to an environment that is more favorable to the sustained production of large oceanic copepods and euphausiids. We propose that long-term changes (4 decades) in the abundance and composition of the seabird community reflect an increase in the availability of large zooplankton prey in the region.

Assessment of the Birds of Swains Island, American Samoa

ABSTRACT Swains Island is an uninhabited 210 ha former copra plantation 360 km North of American Samoa. The island, dominated with coconut palm (Cocos nucifera), was last surveyed in 1976. The goal of this 17–26 September 2012 survey was to identify the bird species present, and document relative abundance, distribution, and breeding activity across the island. Two shoreline surveys recorded a seabird community dominated by Black Noddy (Anous minutus), White Tern (Gygis alba), and Brown Noddy (Anous stolidus), while the reef flat community was dominated by Pacific Golden Plover (Pluvialis fulva) and Wandering Tattler (Tringa incana). Inland surveys revealed four roosting or breeding species, including Black Noddy, White Tern, Brown Noddy, and Red-footed Booby (Sula sula). Seabird densities were highest in the northwest section of the island, furthest from former settlements. Although feral pigs (Sus scrofa) were recently eradicated, feral cats (Felis cattus) remain present, and Pacific rats (Rattus exulan...

In stark contrast to widespread declines along the Scotia Arc, a survey of the South Sandwich Islands finds a robust seabird community

The South Sandwich Islands, in the South Atlantic Ocean, are a major biological hot spot for penguins and other seabirds, but their remoteness and challenging coastlines preclude regular biological censuses. Here we report on an extensive survey of the South Sandwich Islands, the first since the late 1990s, which was completed through a combination of direct counting, GPS mapping, and interpretation of high-resolution commercial satellite imagery. We find that the South Sandwich Islands host nearly half of the world’s Chinstrap Penguin (Pygoscelis antarctica) population (1.3 million breeding pairs), as well as c. 95,000 breeding pairs of Macaroni Penguins (Eudyptes chrysolophus), and several thousand breeding pairs of Gentoo Penguins (Pygoscelis papua). Despite being at the northern edge of their breeding range, we found an unexpectedly large (≥125,000 breeding pairs) population of Adelie Penguins (Pygoscelis adeliae). Additionally, we report that nearly 1900 pairs of Southern Giant Petrels (Macronectes giganteus) breed in the South Sandwich Islands, 4 % of the global population, almost all of which are found on Candlemas Island. We find that the South Sandwich Islands have not experienced the same changes in penguin abundance and distribution as the rest of the Scotia Arc and associated portions of the western Antarctic Peninsula. This discovery adds important context to the larger conversation regarding changes to penguin populations in the Southern Ocean.

Assessing the structure and temporal dynamics of seabird communities: the challenge of capturing marine ecosystem complexity.

Summary Understanding interspecific interactions, and the influences of anthropogenic disturbance and environmental change on communities, are key challenges in ecology. Despite the pressing need to understand these fundamental drivers of community structure and dynamics, only 17% of ecological studies conducted over the past three decades have been at the community level.Here, we assess the trophic structure of the procellariiform community breeding at South Georgia, to identify the factors that determine foraging niches and possible temporal changes. We collected conventional diet data from 13 sympatric species between 1974 and 2002, and quantified intra‐ and inter‐guild, and annual variation in diet between and within foraging habits. In addition, we tested the reliability of stable isotope analysis (SIA) of seabird feathers collected over a 13‐year period, in relation to those of their potential prey, as a tool to assess community structure when diets are diverse and there is high spatial heterogeneity in environmental baselines.Our results using conventional diet data identified a four‐guild community structure, distinguishing species that mainly feed on crustaceans; large fish and squid; a mixture of crustaceans, small fish and squid; or carrion. In total, Antarctic krill Euphausia superba represented 32%, and 14 other species a further 46% of the combined diet of all 13 predators, underlining the reliance of this community on relatively few types of prey. Annual variation in trophic segregation depended on relative prey availability; however, our data did not provide evidence of changes in guild structure associated with a suggested decline in Antarctic krill abundance over the past 40 years.Reflecting the differences in δ15 N of potential prey (crustaceans vs. squid vs. fish and carrion), analysis of δ15 N in chick feathers identified a three‐guild community structure that was constant over a 13‐year period, but lacked the trophic cluster representing giant petrels which was identified using conventional diet data.Our study is the first in recent decades to examine dietary changes in seabird communities over time. Conventional dietary analysis provided better resolution of community structure than SIA. However, δ15 N in chick feathers, which reflected trophic (level) specialization, was nevertheless an effective and less time‐consuming means of monitoring temporal changes.